Atomic Coatings - The Size Of An Atom Lab printable pdf download

Atomic Coatings – The Size of an Atom Lab

AMHS AP CHEMISTRY 2015-16

Introduction: The size of an atom is too small to imagine. Counting the number of atoms in even a microscopic amount of

material is an impossible task – it would take a billion years! It turns out, however, that it is possible to apply a thin surface

coating of metal atoms onto another metal. This is done to change the properties of the underlying or base metal (it is called

electroplating). In this experiment, the thickness of a zinc metal coating on galvanized iron will be determine and used to “count”

the number of layers of atoms in the coating. The number of atoms of zinc will also be determined.

Background: Galvanized iron is produced by coating iron with a thin layer of metallic zinc. The zinc coating protects the

underlying iron metal against rusting and corrosion. Zinc is more reactive than iron and thus reacts with oxygen in the air and

with water before the iron does. In this way, the zinc coating prevents oxygen from reaching the iron. The greater reactivity of

zinc continues to protect the iron even after the surface of the zinc has been broken or breached. Galvanized iron has many

applications, including rain gutters, heating ducts, nails and screws, etc.

The amount of zinc deposited on the surface of galvanized iron can be determined by reacting the zinc with hydrochloric acid.

Write the appropriate equation in the space below.

Equation 1:___________________________________________________________________________________

The products of the reaction are zinc chloride, which dissolves in the hydrochloric acid solution, and hydrogen gas, which bubbles

out of the solution. By measuring the mass of a piece of galvanized iron before and after its reaction with hydrochloric acid, the

mass of zinc that reacted can be calculated. The mass of zinc can be related, in turn, to the number of layers of zinc atoms in the

zinc coating by considering the density of the metal, the surface area of the galvanized iron, and the size of a zinc atom.

Purpose of this experiment is to: a) determine the number of layers of zinc atoms in the protective coating on a sheet of

galvanized iron; b) determine the number of moles of zinc and the number of atoms of zinc in the protective coating; c) determine

the volume of hydrogen gas produced based on the current conditions; d) determine the enthalpy values associated with the

chemical reaction.

Safety: Hydrochloric acid solution is toxic by ingestion or inhalation and is severely corrosive to skin and eyes. Avoid contact

with skin and eyes. The pieces of galvanized iron may have sharp edges that can cut skin. Wear goggles and aprons. Wash

hands with soap and water after lab.

Pre-Lab Questions:

1. What is the purpose of coating the galvanized iron with zinc?

2. The reaction represented by Equation 1 must be carried out until all of the zinc has reacted. What visible sign of the reaction

can be used to determine when all of the zinc has reacted? (Hint read procedure step 5) What may be responsible for this color?

(You may need to research this answer while considering the metal(s) present.)

3. How many moles of zinc are present in a 2.00 gram sample? How many atoms are present? What mass of hydrogen gas

would be produced if the reaction occurred on this sample but was only 85.0% efficient?

Procedure:

1. Obtain a piece of galvanized iron and measure and record its mass using a balance. (Caution, the edges are very sharp!)

2. Measure the length and width of the piece of galvanized iron using a metric ruler and record. (You may need to assume the

piece is a perfect square or rectangle for simplicity sake.)

3. Place the metal piece in a beaker large enough for it to lie on the bottom of the beaker and add enough 6M hydrochloric acid to

cover the metal (about 25mL). Note the approximate temperature of the outside bottom of the beaker with the back of your hand.

4. Let the beaker stand until the rapid bubbling stops. Check the temperature of the beaker again (as in #3) and record.

5. When the signs of reaction indicate that all of the zinc has reacted, add about 200 mL of tap water to the reaction beaker. This

will dilute the hydrochloric acid solution and stop the reaction. [Note: When the reaction is complete, the piece of galvanized

iron will begin to discolor and the solution will turn a pale green color.]

6. Place the beaker in the sink and gently begin adding water from the tap (Caution: do not spray a strong stream of water into

the beaker!). Continue to add water until the beaker overflows and the metal is completely rinsed of residual acid.

7. Carefully remove the sharp metal from the beaker and dry the metal on a piece of paper toweling. When the metal is

completely dry, measure it’s mass again and record the value in the data table.

Atomic Coatings - The Size Of An Atom Lab

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